GenealogyBank.com has the Omaha World-Herald newspaper online for 1921. I checked the Births column for May 6-18, 1921 but did not find the births of any twin boys. The lists include both hospital and home births. Each entry includes the baby's gender, parents' names, address and whether the birth occurred in a hospital. There was one set of twins--girls--born in Ralston, an Omaha suburb now. What is not included is the date of birth and I don't know the lag time for publishing these. So while this isn't proof the boys were not born in Omaha, the lack of a listing for twin boys suggests the births could have occurred elsewhere. Best of luck in your research!